1. Field of the Invention
The present invention relates to the field of film deposition, and more particularly to a method and apparatus for evaporation depositing uniform thin films, and both method and apparatus maintain a constant evaporation rate to improve the uniformity and quality of the thin films.
2. Description of the Related Art
Vapor deposition is applied extensively in the industry for manufacturing components composed of thin films such as organic light emitting diodes (OLED) and thin film solar cells. In general, the vapor deposition is applied in a vacuum system to place an evaporation material in an evaporation vessel and use a heater to heat the evaporation material, such that the evaporation material is evaporated and volatilized to achieve the effect of forming a thin film on an evaporation material.
In the vapor deposition process, the following issues are confronted frequently: 1. Since the evaporation material is in contact with a vacuum environment system directly through an evaporation source spout. From the related literature “Ind. Eng. Chem. Res. 2009, 48, 5975-5991, Ind. Eng. Chem. Res. 2009, 48, 5992-5999”, the evaporation material gradually decreases with time, and the drop of the level of an evaporated liquid causes a temperature difference between the center and the edge of the evaporation vessel and results in a change of the deposition rate, so that the process cannot be controlled or quantized effectively. 2. To achieve the purpose of mass production, the vapor deposition process usually adopts the design of a linear evaporation source for the film deposition to obtain a large thin film, particularly an absorbing layer of a copper-indium-gallium-selenium thin-film solar cell, and requires a plurality of independent evaporation sources to carry out the mixing and evaporation of the evaporation material as disclosed in U.S. Pat. Nos. 2010/0285218A1, 2010/0159132A1, U.S. Pat. Nos. 7,968,353B2, 8,202,368B2, 7,194,197B1, 2009/0255469A1, 2009/0258444A1, 2010/0087016A1, 2009/0258476A1, 2013/0045563A1 and U.S. Pat. No. 7,194,197B1. In these mixed vapor deposition processes, different evaporation materials may cause a non-uniformity of the thin film coated on the evaporation material according to the different evaporation distances from the center of each independent linear evaporation source, and the linear evaporation sources may interfere with one another during the mixing and evaporation process of the evaporation material due to the evaporation angle of each linear evaporation source, so that the uniformity of the thin film is reduced significantly. 3. The depth profile of the produced thin film may be non-uniform when the evaporated material moves in a roll-to-roll or flow manner in a direction perpendicular to each independent evaporation source.
In view of the aforementioned drawback of the conventional film deposition, the inventor of the present invention provides a method for stably evaporation depositing uniform thin films to produce the thin films with high stability, uniformity and production quality.